FIG. 1 shows an example of the conventional control system for controlling the electric equipment provided with step motors, a print hammer (hereinafter to be simply described as hammer), and the like using a microprocessor circuit. In this example, the control system is to control the step motor action and the hammer action for use in a printer. Reference numeral 1 in FIG. 1 is a plug to be connected with commercial AC power source. Reference numeral 2 is a power transformer to convert a commercial AC power voltage into the voltage for logic circuit or into the voltage for electric equipment drive. Reference numerals 3 and 4 are rectifiers, the former being used to convert an AC voltage for the logic circuit into a required direct current and the latter to convert an AC voltage for driving the electric equipment into a required voltage. The DC voltage thus converted through rectifier 3 is further stabilized by voltage stabilizing circuit 5, and reaches microprocessor circuit 6 and quartz oscillating circuit 7. On the other hand, the DC drive voltage for electric equipment thus converted through rectifier 4 is further stabilized by voltage stabilizing circuit 8, and then splits into two ways, one reaching drive circuit 10 for step motor 9 and the other reaching drive circuit 12 for hammer 11. Microprocessor 6 receives a pulse signal as a periodic clock signal output from quartz oscillator 7, is activated by this clock signal, and outputs a predetermined signal to drive circuits 10 and 12 to activate step motor 9 and hammer 11, respectively. Thus, the electric equipment drive control system of the prior art is provided with two voltage stabilizing circuits 5 and 8 to obtain a required voltage for the logic circuit and a required drive voltage for electric equipment. Therefore, if the power voltage inputted to power transformer 2 via plug 1 varies, quartz oscillator 7, microprocessor circuit 6, and the electric equipment (step motor 9, and hammer 11) act normally.
In general, the power circuit for direct current stabilizing is of two types, a dropper type and a switching type. The former requires a voltage transformer equipped with a radiator, thereby radiating waste energy and resulting in low energy efficiency. The latter is superior in energy efficiency but it is likely to generate noise and is expensive due to the complexity of its circuit. In any case, such direct current stabilizing circuits are costly and energy inefficient. If such voltage stabilizing circuits are removed, the power voltage which has been changed in applied directly to the electric equipment circuit. Moreover, the microprocessor circuit is designed, based on a prescribed voltage value, to calculate a lapse of time throughout which power is applied to each circuit of the electric equipment. In consequence, if the power voltage is small, that is, if the electric equipment is the step motor, for example, it may reduce the torque of the motor, which in turn may cause, the step motor to malfunction, and if the electric equipment is the printer hammer, it may cause the printed character to be too thin. On the other hand, if the power voltage is large, the electric equipment carries out unnecessarily excessive work, resulting in consumption of excessive and wasted energy.